I have two windows services. One ('server') acts as a WCF host to which the other ('client') connects. So I have configured a dependency from client to server. Both are also set up to start automatically.
When I start these services by hand, everything works fine. When I stop both services and tell client to start, then server will be started before client and all is fine.
However, when I reboot the machine only server is started.
When I add a diagnostic listener I see it got a TimeoutException with the helpful message:
The HTTP request to 'http://[server address]' has exceeded the allotted timeout of 00:00:00. The time allotted to this operation may have been a portion of a longer timeout.
At some other SO question there was an answer that claims WCF is probably confused about what went wrong and therefore starts lying about the timeout.
Did I perhaps miss a dependency for either service? Does WCF require something that hasn't or is being started when client is trying to contact server?
I think you should check your client service. On startup windows services are starting while network devices are still being initialized. Services should be ready to start without network and without any network device. Usual approach is to keep periodic retries to establish connection. You can do little experiment on your machine by uninstalling all network adapters and trying to start up your services.
Additional quick workaround you can do is to setup recovery options on your service -- for example you can configure it to restart service on crash after some timeout -- you can do this through UI in services.msc or in command line using 'sc config' command.
Configuring the dependency between the two Windows Services is not necessarily sufficient to avoid there being a race condition: i.e. to avoid the client service calling the WCF service before the server's WCF channel stack is fully initialised.
The service dependency just ensures that the Windows Service Control Manager won't start the client service process before the server Windows Service has notified the SCM that it has started. Whether this is sufficient depends on how you write the server.
If the server service starts a new thread on which to initialize the WCF stack, your OnStart method is probably returning before the WCF stack is ready for clients. There is then a race condition as to whether the client's first call will succeed.
On the other hand, if the server service does not return from OnStart (and thus doesn't notify the SCM that it has started) until the channel stack is fully open, the dependency removes the race condition, but there is a different pitfall: you need to beware that the SCM's own timeout for starting the Windows service is not triggered while waiting for the WCF stack to initialise, as might well happen on a reboot if the WCF service depends on the network stack, for example. If the server's OnStart does not return within the SCM's timeout, the SCM will not try to start the dependent client service at all, because it does not receive the server's start notification. (There will be a message in the Windows event log from the SCM saying that the server service didn't start within the expected time.) You can extend the SCM timeout by calling ServiceBase.RequestAdditionalTime while the WCF service is being initialised.
Either way, the client service really ought to be written so that it doesn't fail completely if the first WCF call doesn't succeed.
You don't actually say what binding you are using. If client and server services are always running on the same machine, as you seem to indicate, then consider using the NetNamedPipeBinding: then your service won't be dependent on initialization of networking resources and startup should be quicker.
Related
I'm developing a client/server app in which the client calls the WCF service every few seconds. I'm not using IIS - the service runs as a console app (with the intention of installing it as a Windows service on production systems).
I started off using basicHttpBinding, and if I stop the service (to simulate a comms/server failure) the client simply ignores the fact that it can't connect to the service, by handling the EndpointNotFoundException that gets thrown. After restarting the service, the client is able to start calling it again and everything is good.
I've now switched to using netTcpBinding, and this time when I stop the service it takes a little while for its console window to close (presumably due to the way TCP manages the connection, which eventually times out). At this point the client gets a CommunicationException ("the socket connection was aborted"). When I restart the service, the client isn't able to "resume" like it did with basicHttpBinding. Each time it tries to call the service it throws a CommunicationObjectFaultedException ("The communication object, System.ServiceModel.Channels.ServiceChannel, cannot be used for communication because it is in the Faulted state.").
How would I go about building in some kind of resume/recovery behaviour, similar to what I saw with basicHttpBinding?
You cannot reuse the channel as it has faulted. You should cast your client to an ICommunicationObject and call Abort() to clean up.
After that you simply start afresh by creating a new client channel. You may want to do this on a timer if your server is down for a period of time.
I have a fairly straightforward WCF service that performs one-way file synchronization for a bunch of smart clients. I've noticed that when there's a network or service interruption during a call, the client stops being able to communicate with the server until the entire application is restarted.
The service runs with BasicHttpBinding and is hosted with IIS6 (a .svc page), using transferMode="Streamed" and messageEncoding="Mtom". The service is configured to use the default InstanceContextMode (I think it's Per Call?) and ConcurrencyMode=Single. It's using the default throttling behavior, but I'm in an isolated test environment that nobody else is hitting.
Clients are Windows Services. I'm using this ServiceProxyHelper to ensure connections are Close()'d or Abort()'d correctly when Dispose()'d, though there are no sessions so I don't think that even matters. When an error occurs, the Client object is disposed and then goes out of scope. After the exception is detected, the service waits a bit, then creates a new client object and tries again. So it should recover from the failure, but for some reason all subsequent calls to the service fail.
I can reproduce this reliably by starting a client, allowing it to transfer a few files, then iisresetting the server. First the client generally displays a "Service is Too Busy" error (which maps to the IIS 503 error that you get during an app restart). After that, all subsequent calls to the service time out. As far as I can tell the calls are not even being attempted by the client. I have tracing enabled and what I see is: Timeout error, followed by a "Failed to send request message over HTTP" warning, followed by another Timeout error.
The crazy thing is that when I configure the client to use Fiddler (port 8888) as a proxy in app.config, everything works as desired. So somehow Fiddler as the proxy is closing or finalizing some kind of connection that WCF on its own is not.
Thoughts?
Edit 2009-10-30 8:54PM: Changed service attributes to: InstanceContextMode=Single and ConcurrencyMode=Multiple. No difference.
Well that was painful. It took me forever but finally I zeroed in on the difference between running with a proxy vs without and started poking around the <system.net> settings. It turns out that adding this configuration bit to the client fixes the problem:
<system.net>
<settings>
<servicePointManager expect100Continue="false" />
</settings>
</system.net>
Can somebody explain what's going on? Why should this setting cause WCF clients to hang irreparably when there's a service interruption?
Are you sure this isn't a client side issue. If your Windows service is making the WCF calls on a seperate thread from the main, and you have an un-handled exception happening on the child thread...the calling thread may or may not sit there and wait forever becaues it's waiting for that thread to return.
That would explain why there's an Exception inside the service and then it looks like the service makes no more calls to the service...it's hung.
Used to be a huge issue when using Timers to spawn processes in .NET 2.0 Windows Services.
My application has 50 service endpoints (such as /mysite/myService.svc). It's hosted in IIS. Intermittently (once every two or three days) a service stops responding. It's never the same service that hangs. While a service is hung, some of the other services work fine and some other are also hung.
All clients (from different computers) get this error:
ServiceModel.CommunicationException
Message: An error occurred while receiving the HTTP response to
https://server/mysite/myservice1.svc.
This could be due to the service endpoint binding not using the HTTP
protocol. This could also be due to an HTTP request context being
aborted by the server (possibly due to the service shutting down).
See server logs for more details.
No exceptions are raised by the server when the client attempts to call the service that is hung. All I have is that error on the client side.
I have to manually recycle the application pool to fix the problem.
Do you know what could be the cause? How can I investigate this issue? I'm willing to take a memory dump of the worker process when a service is hung but I would not know what to search for in the dump.
Update (Aug 13 2009): I have almost ruled out the idea that the server runs out of connections (see comment in Shiraz Bhaiji's answer). I might have a new lead: I log all server-side exceptions in a log file. So in theory, when this occurs on the client, no exceptions are raised on the server; otherwise I'd have proof of that in my logs. But what if an error does occur on the server but is happening at a low level where exceptions are not routed to my exception handling code? I have posted this question about scenarios where low level exceptions cannot be handled. I'll keep you informed of the progress of my investigation.
Sounds like you are running out of connections.
By default WCF has a timeout and therefore holds a connection open for 10 mins.
When you recycle the app pool all connections are closed, and therefore things work again.
To fix it check your code to make sure that you close connections / dispose of proxies.
To resolve this, we set establishSecurityContext to False on the binding.
I have not come across this particular issue but would suggest to turn on tracing/message logging for the WCF service in the config for the service and/or the client app (if you have control over that). I've done this in the last few days for a service that I needed to troubleshoot.
The MSDN link here is a good starting point.
Also see the table in this post for the varying levels of trace detail you can configure. There are several levels which can go from exception only logging to full message details. It is quite quick to set this up in the app.config file.
To parse the log file output use the SvcTraceViewer.exe that comes with the Windows SDK, which if you have it installed should be located in this folder: C:\Program Files\Microsoft SDKs\Windows\v6.0\Bin
I have 2 wcf services, 1 which polls the other service at regular interval.The service2 is hosted in no. of machines with the same configuration.
My problem is that whenever the poller service gets restarted, even though the service2 on other machines runs fine, i am not getting the response from those services (basically it gets timed out - getting SYSTEM.TimeOutException ). If I try to access the same service (service2) from some temp application (without restarting the service2) it gives response.
If I restart the service2, than it works fine, the service1 (poller service) gets the responses from all hosted services (Service2).
Dont know what is causing problem.
Regards,
Chirag
Attach VS to your wcf service which hangs. And find out if your connection is successful.
Do it with both services, so that you can debug the services at runtime.
If you're using a sessionful binding (netTcpBinding, wsHttpBinding), it's more than likely that you're not explicitly closing your client channel when you're done with it. This would cause the behavior you see, because the session takes a minute or so to time out if you don't explicitly close it, and the default max number of sessions is low (10)- the server will let new sessions stack up until old ones close. You can also adjust the service throttle on the server side binding to increase the max number of open sessions allowed, but you really should make sure your clients are getting cleaned up properly first.
I have a WCF Service that I have written, which is hosted within a Windows service. It is operating in PerSession mode. The service permits clients to open files, make changes to files and close files remotely through the service. So far all works very smoothly.
When the Windows service is stopped, I would like to be able have the WCF Service not accept any new sessions and yet allow already connected clients to complete their current sessions and work (within a reasonable period/timeout).
What would be the best way to accomplish this?
Basically, calling ServiceHost.Close() will accomplish this - it will let all currently running request run to completion, but new request are being rejected will the orderly shutdown is in progress.
There's a "CloseTimeout" setting on your binding that you configured for your service - that controls how long the WCF runtime will allow running requests to take until they've properly shut down. If that timeout happens, the still running requests will be killed.
The ServiceHost.Abort() method on the other hand is the digital equivalent of a sledgehammer - all running requests are terminated at once, and the host is shut down.
ON the client side, you have the same .Close() and .Abort() methods on your client proxy which behave the same way.